Now, there are many skills that make stacks, for example Relequen and Siroria. Those logs however are basically useless in Combat Metrics and takes 20 lines. I mean it is not very useful to know how many % of fight you had 7 stacks of Relequen... If technically possible (calculation shouldn't be overly complicated), I would suggest that CMX counts the average attack/spell powers you get from those for fight duration.